Postal blue ink with improved durability

ABSTRACT

A water-based ink for inkjet recording exhibits a blue color defined as L*&lt;45, 25&lt;C*&lt;28, 255&lt;h&lt;278, and comprises a mixture of dyes and pigments, specifically including C.I. Pigment Blue 60 and C.I. Acid Blue 90, with water and a water-soluble organic solvent. The blue ink provide an image which has good water resistance and high optical density.

RELATED APPLICATIONS

The present application is related to U.S. application (Attorney DocketG-435) Ser. No. ______, entitled “Postal Blue Ink with HighReliability”, filed on the date of this application, the applicationincorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The invention disclosed in the illustrative embodiments herein relatesgenerally to blue postal inks adapted for inkjet printing and capable ofproviding clear images on a broad range of substrates, meeting a varietyof competing requirements necessary for postal use.

BACKGROUND OF THE INVENTION

It has been a common problem that posts, especially the major EuropeanPosts, have adopted the color blue for their franking inks. Thisdecision was due to the larger absorbance range of the blue in thevisible spectrum as opposed to red inks. Most of the detectors in theavailable postal scanners are optimized for OCR mainly in black and,therefore, will be more suitable to detect blue than red. Since variousEuropean Posts have different and sometimes contradictory requirements,there is a need for a single ink that will satisfy all European andpossibly other postal requirements.

One important requirement which is contradictory to others, is forextremely high contrast on porous substrates (>70%) while keeping thecolor blue with certain limits for the color parameters contradictingthe high contrast requirement. Blue does not inherently exhibit highcontrast, and the formulation modifications necessary to achieve a bluecoloration on some substrates will not necessarily work on others.

Other contradictory parameters working against the identification of asingle blue postal ink are the need durability in terms of waterfastnessalong with high contrast (high loading of the colorant) and reliability(decap time, purging). An important attribute of inkjet ink is “decap”time, i.e., the time a nozzle can remain dormant and then still fire adrop without misdirection or loss of velocity. Decap is to some extentaffected by ink vehicle evaporation which leaves behind a deposit ofnonvolatile ingredients that are detrimental to jetting performance. Inother words, to achieve waterfastness and high contrast, it may benecessary to provide high concentrations of pigment and/or dyes, andthis can adversely affect purging and decap properties.

There is a clear need for a blue postal ink for inkjet printing that iscapable of providing durable, high contrast, machine-readable images,especially those containing bar code information, on a broad range ofsubstrates while meeting a diverse array of regulatory requirements.

SUMMARY OF THE INVENTION

The present invention provides blue inkjet ink compositions and methodsof printing and printed substrates employing them.

The blue ink compositions of the invention are water-based inks forinkjet recording and comprise colorant mixtures comprising C.I. PigmentBlue 60 blue pigment and C.I. Acid Blue 90 dye, preferably incombination with water-soluble organic solvent such as glycerol adispesant, and water. The ink compositions of the invention arecharacterized by printing images with good durability. They can exhibithighly reliable print head operation, especially in terms of printingwithout capping, and preferably meet many other, often contradictoryperformance criteria, including, inter alia: printing on diverseenvelope surfaces, readability of 2D bar codes on porous and coatedsubstrates, blue color defined as L*<45, 25<C*<28, 255<h<278,waterfastness, drying time, lightfastness, and abrasion resistance.

In one aspect, the inks of the invention comprise: a colorant mixturecomprising C.I. Pigment Blue 60 and C.I. Acid Blue 90, preferably incombination with red and yellow dyes; triethylene glycol monobutyl etheras a penetrant, a styrene acrylic copolymer as a polymeric dispersant,glycerol as water-soluble organic solvent, and water.

In another aspect, the invention provides a process for printing animage having a visible, blue image with at least 70% contrast,comprising: providing a piezoelectric or thermal inkjet printer with anink as described in above, and printing an image with the ink on asubstrate.

In another aspect, the invention provides printed image prepared by theprocess described above.

Other preferred and alternative aspects of the invention will bedescribed below.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The present invention provides blue inkjet ink compositions and methodsof printing and printed substrates employing them.

The blue ink compositions of the invention include colorant mixtures toproduce machine readable images by inkjet printing having a blue colordefined as L*<45, 25<C*<28, 255<h<278 and enable meeting many, oftencontradictory performance criteria. Preferably, the ink compositions ofthe invention meet at least two of the following criteria, and mostpreferably meet them all:

-   -   waterfastness, preferably of at least about 80% of original        optical density (OD), obtained by measuring the optical density        of a solid block area 24 hours after printing, and again after        soaking in deionized water for 5 minutes and drying (Ref.        ISO18935-2005(E)) (using a K 700 postage machine and an optical        densitometer RD914 with a visual filter);    -   drying time of less than about 1 second for a US Type A envelope        and less than about 10 seconds for a German No. 1 envelope,        drying time being the time for the image to be sufficiently dry        that no smear occurs by rubbing with a cotton swab (using a K        700 postage machine);    -   lightfastness, preferably of at least about 90% of original        optical density, obtained by measuring the optical density of a        solid block area and the blue scale 2, 24 hours after printing,        and again after exposure to xenon light for 23.5 hours (Ref.        ISO2835-1974(E)) (using a K 700 postage machine, Xenon        lightfastness tester Blue scale 2, and an optical densitometer        RD914 with a visual filter); and    -   good jettability, which means that printing occurs from all        nozzles after a print head is left uncovered at 60° C. and 40%        relative humidity for a day after printing and then purged        (cleaned).

Desirably, the ink compositions of the invention will be capable ofprinting images with at least 70% contrast on diverse envelope surfaces,with at least 99% machine readability of 2D bar codes on porous andcoated substrates. They are used in the conventional manner to printimages by inkjet printers of the thermal and the piezoelectric types.The printed images are of superior quality in terms of color,durability, waterfastness, light fastness and/or drying time.

Inks according to the invention for use as inkjet inks are desirablystable chemically in aqueous solution and have effective viscosity andsurface tension characteristics to assure satisfactory operation of thedesignated type of inkjet printer. Printers can be of the piezoelectricor bubble type. The viscosity of the liquid inks used in currentpiezoelectric inkjet printers is typically from 1.5 to 20 centipose(cps) and in the thermal inkjet printer is lower, e.g., from 1 to 5 cps.The desirable surface tension of liquid inkjet printer inks willtypically be between 30-45 dynes/cm.

Experience has shown that printing in the desired color blue isespecially difficult to achieve while also maintaining compliance withcontradictory requirements from various Posts that require a high levelof waterfastness, and very high contrast on porous media. In additiondue to high processing speeds for a practical postal ink, there is aneed for fast drying inks; and this can be also contradictory to meetingcontrast criteria.

The new formulations of the invention are hybrid inks, which mixessential pigments and dyes, with some discretion as to optionalcolorants, to achieve the desired contrast and hue to enable desirableresults on a broad range of substrates.

The following table identifies a range of substrates for which the inksof the invention have been shown to be effective in printing with acontrast of at least about 70% while also meeting other importantcriteria.

TABLE 1 Country and Porosity Smoothness Cobb Sizing Envelope Number(Sheffield) (Sheffield) (g/m²) pH DE 1 164 143.4 30 7.97 DE 2 98.8 254.122 7.26 DE 3 125 228.4 24 7.31 DE 4 36 19.3 51 8.71 DE 5 36 84.5 82 8.86FR EN2003 — — 30 — FR EN1615 55 206 55.3 — FR EN1618 93 217 32.1 — FREN1977 94 287 28.3 — FR EN3745 40 179 40 — USA 148 175 140 8.58

The inks of the invention will have a tightly defined blue color as isnecessary to meet the visual and contrast requirements for the purposeof postal franking. The blue color is defined as L*<45, 25<C*<28,255<h<278. The CIE L*C*h is the cylindrical version of CIELUV and isknown as CIE LCH_(uv), where L* is the lightness, C* is the chroma and his the hue. According to CIE (International Commission on Illumination)standards the CIE 1976 (L*, u*, v*) color space, also known as theCIELUV color space, is a color space adopted by the InternationalCommission on Illumination (CIE) in 1976, as a simple-to-computetransformation of the 1931 CIE XYZ color space, but which attemptedperceptual uniformity. It is extensively used for applications such ascomputer graphics which deal with colored lights. Although additivemixtures of different colored lights will fall on a line in CIELUV'suniform chromaticity diagram (dubbed the CIE 1976 UCS), such additivemixtures will not, contrary to popular belief, fall along a line in theCIELUV color space unless the mixtures are constant in lightness.

The inks of the invention provide excellent readability of 2D bar codeson porous and coated substrates as measured by Integra Verifier (gradeA) with red filter.

As noted, the new ink formulations of the invention are hybrid inkswhich mix pigments and dyes. The inks of the invention overcome aproblem associated with high-pigment content formulations, which canhave adverse effects on maintenance in terms of built-in purging andwiping systems. On the other hand, entirely dye based systems will notprovide images with the necessary waterfastness. The inks of theinvention will typically contain at least about 4% by weight of acolorant mixture comprising a mixture of specific dyes and pigments, andwill provide images with good durability.

The ink compositions of the invention will include C.I. Pigment Blue 60and C.I. Acid Blue 90, to achieve the color defined above. Also usefulare red dyes, such as Acid Red 289, yellow dyes, such as Acid Yellow 23,magenta dyes such as Pigment red 122, carbon black and other optionalpigments, such as cyan Pigment Blue 15:3, in total of no more than aminor amount, e.g., less than about 25%, based on the combined weight ofthe Pigment Blue 60 and the Acid Blue 90. The colorants exemplifiedbelow and others chosen as effective within this description will allprovide the blue color defined as L*<45, 25<C*<28, 255<h<278, and willprovide the desired contrast when formulated in accord with thisdescription.

The inks employ a penetrant, preferably triethylene glycol monobutylether (TGMBE, molecular weight of 206), as well as anionic surfactantsin the formulations of the invention facilitate the desired drying timewithout destabilizing the dispersion of pigments.

The blue ink compositions of the invention are water-based inks forinkjet recording and comprise colorant mixtures in combination withglycerol as water-soluble organic solvent, preferably in an amount offrom about 20 to about 30% by weigh of the ink composition. Otherpolyols may also be comprised in the water-soluble organic solvents. Theinks will comprise water, preferably in an amount of at least about 40%,e.g., from about 50 to about 70%, of the weight of the compositions.

The amount of the water-soluble solvents compared to the colorants canbe important to obtain the best properties for jettability along withimage properties, and preferably the weight ratio of a total amount ofwater-soluble organic solvent to an amount of C.I. Pigment Blue 60 is8:1 or more and, preferably less than about 15:1. The examples whichfollow provide a guide to most effective relative amounts. Preferably,an amount of C.I. Pigment Blue 60 relative to a total amount of thewater-based ink is in the range of about 0.1% to about 5% by weight.Typically, the colorant, which is a mixture, comprises at least 4% byweight of the composition and the Pigment Blue 60 will comprise at least1% by weight of the composition. Using the examples as a guide, it canbe seen that inks employing a ratio of pigment to dye in the colorant iswithin the range of from about 1:2 to about 2.5:2, will be effective.

The inks also employ a polymeric dispersant for stabilizing thedispersion and preventing coagulation or displacement by othercomponents such as, for example, the dye used.

Another characteristic important to the proper functioning of the inksof the invention is compatibility with other inks because seamlessmixing is a very challenging target and one that is critical to imagequality. The present ink concept achieves this goal by employingspecific colorants and having bridging components such as the polymericdispersant, which is preferably one selected from the group consistingof acrylic polymer, styrene acrylic copolymer, styrene Maleic copolymerand styrene methacrylic copolymer. The preferred polymeric dispersant isstyrene acrylic copolymer (e.g., as JONCRYL 62J from BASF, available asan aqueous solution with 34% nonvolatiles and a viscosity of 2,500 cps),and is preferably employed in the inks of the invention in an amount offrom about 0.5 to about 10% by weight of the composition, typicallybeing from 1 to 3%. Using the examples as a guide, it can be seen thatinks employing a ratio of the dispersant to colorants within the rangeof from about 4:10 to about 7:10, will be effective.

Reliability is an important attribute and advantage of the inks of theinvention. Before the invention, it appeared that the achievement ofinks with all the necessary print performance qualities using pigmentsor hybrid mixtures would have a tendency to dry more at the nozzles andto precipitate and cake formation around the nozzle plate. These oldinks are not reliable. However, the invention provides reliability inthe formulations due to the hybrid character of the inks, the use ofresolubilizing resin combined and a compatible water-soluble organicsolvent blend comprised of specific polyols. The combination of thespecific water-soluble organic solvents with the polymer dispersant iseffective in maintaining an equilibrium at the nozzle interface andprovides consistent redispersability of cake formed at the nozzle. Thenet effect, in addition to the contradictory and diverse print qualityrequirements (e.g., color, readability, waterfastness, light fastness,drying time, print growth, and the like), is the provision ofpredictable performance and high quality over time.

Among other ingredients of the inks of the invention are surfactants.Among these are ionic and nonionic species. Anionic species such assodium alkyl sulfonates, cationic surfactants such as cetyltrimethylammonium bromide, zwitterionic surfactants such assulfobetaines, and non ionic surfactants such as alkyl polyethyleneoxides (e.g., available as Igepals), non-ionic acetylenic diolsurfactants (e.g., surfinols), etc., can be employed, at effectivelevels, with preferred surfactants being anionic surfactants such asdodecylbenzenesulfonic acid sodium salt. Representative surfactantconcentrations will be from about 0.2 to about 2.0% of the weight of thecompositions.

Another important characteristic achieved by this new inks is the shelflife (1 to 2 years) by preventing undesirable particulate formation byaccelerated aging.

In another aspect, the invention provides a process for printing animage having a visible, blue image with at least 70% contrast,comprising: providing a piezoelectric or thermal inkjet printer with anink as described above, and printing an image with the ink on asubstrate. As noted above, it is an advantage of the invention that theinks can print images on a wide variety of substrates in the desiredblue color and with high contrast and durability and still provideexcellent jettability. The examples below further illustrate thisadvantage.

In another aspect, the invention provides printed images prepared withthe inks and by the process described above. It is an advantage of theinvention, as pointed out above, that the images can be printed on awide variety of substrates in the desired blue color and with highcontrast and durability as noted.

The following examples are presented to further illustrate and explainthe invention and are not to be taken as limiting in any regard. Unlessotherwise indicated, all parts and percentages are by weight.

EXAMPLES

Below are comparisons of the new formulations tested for jettabilityagainst other, apparently similar ink formulations.

The following table summarizes results of tests, which show theimprovements of the ink compositions of the invention for achievingsuperior jettability, which is a key factor in printer reliability. Inthe examples, water makes up the balance of the 100% of theformulations.

TABLE II Formulations Example Comparative Example 1 2 3 1 2 3 4 5 C.I.Pigment Blue 60 2 2 3 4 2 2 C.I. Pigment Blue 15:3 3 Dispersant Polymer,2.5 2.5 3.75 5 2.5 2.5 2.5 JONCRYL 62J from BASF C.I. Acid Blue 90 2.8 22 2.8 4 C.I. Acid Blue 9 2.8 Projet Fast Cyan 2 2.8 (FujiFilm ImagingColorants) Glycerol 21 21 21 21 21 21 21 21 C.I. Acid Red 289 0.17 0.70.7 0.17 0.17 0.17 0.17 C.I. Acid Yellow 23 0.12 0.1 0.12 0.12 0.12 0.120.12 Triethyleneglycol monopropyl ether 2 Triethyleneglycol monobutylether 2 5 5 2 2 2 2 Anionic surfactant, 0.5 0.05 0.05 0.05 0.5 0.5 0.50.5 Dodecylbenzenesulfonic Acid Sodium Salt

TABLE III Testing Example Comparative Example 1 2 3 1 2 3 4 5 Envelope(FR EN#) 2003 2003 2003 2003 2003 2003 2003 2003 Optical Density, beforetest 0.82 0.83 0.85

0.86 0.92 0.78 Optical Density, after 5 minute 0.79 0.8 0.85 0.59 0.690.85 0.6 0.64 water soak Remaining Optical Density, % 96 96 100 98 91 99

2D Readablity, bleach Before Pass Pass Pass Pass Pass Pass Pass Passtest plus wiping effects After — Pass Pass Pass Pass

Pass Pass Envelope - DE # 1 1 1 1 1 1 1 1 Optical Density, before test0.88 0.9 0.93 0.67 0.8 0.92 0.94 0.8 Optical Density, after 5 minute0.85 0.89 0.91 0.66 0.75 0.9 0.64 0.68 water soak

The results shown in underlined bold italic in the above table arefailures, indicating that variation from the combination of Pigment Blue60 and Acid Blue 90 as provided according to the invention will notprovide the desired combination of properties, including printdurability.

While the present invention has been disclosed and described withreference to a single embodiment thereof, it will be apparent, as notedabove that variations and modifications may be made therein. It is alsonoted that the present invention is independent of the machine beingcontrolled, and is not limited to the control of inserting machines. Itis, thus, intended in the following claims to cover each variation andmodification that falls within the true spirit and scope of the presentinvention.

1. A water-based ink for inkjet recording having a blue color defined asL*<45, 25<C*<28, 255<h<278, comprising: a colorant including C.I.Pigment Blue 60 and C.I. Acid Blue 90, water-soluble organic solvent andwater.
 2. The water-based ink according to claim 1, wherein an amount ofC.I. Pigment Blue 60 relative to a total amount of the water-based inkis in the range of 0.1% by weight to 5% by weight of the composition andan amount of C.I. Acid Blue 90 relative to a total amount of thewater-based ink is in the range of about 0.1% by weight to 5% by weightof the composition.
 3. The water-based ink according to claim 1, whereinthe colorant comprises at least 4% by weight of the composition.
 4. Thewater-based ink according to claim 2, which further includes a polymericdispersant and the ratio of the dispersant to colorants within the rangeof from 4:10 to 7:10.
 5. The water-based ink according to claim 4,wherein the ink provides images with at least 70% contrast on diverseenvelope surfaces, with at least 99% readability of 2D bar codes onporous and coated substrates.
 6. The water-based ink according to claim4, wherein the ratio of pigment to dye in the colorant is within therange of from 1:2 to 2.5:2.
 7. The water-based ink according to claim 4,wherein the water-soluble organic solvent is present in an amount offrom about 20 to about 30% by weight of the ink.
 8. A process forprinting an image having a visible, blue image with at least 70%contrast, comprising: providing a piezoelectric inkjet printer with anink as described in claim 1, and printing an image with the ink on asubstrate.
 9. A printed image prepared by the process of claim 8.